Age-related macular degeneration (AMD) is the leading cause of irreversible visual impairment among the elderly, a segment of the population which is rapidly increasing. There is some suggestion that AMD has a genetic component, but data are sparse. We propose to investigate the genetic contribution to AMD among twins enrolled in a large and well-characterized systematic sample of twins. Twelve thousand four hundred twins representing 6200 pairs with both members alive, ages 67 to 77 will be included. Prevalent cases of AMD will first be identified by a telephone screen, followed by an ocular medical record review. Affected twins and all co-twins will then have an ocular examination and fundus photography. Based on pilot screening data in this registry to date, we estimate that 300 pairs with at least one member having AMD will be enrolled in this study. The contribution of genetic susceptibility to AMD will be evaluated by comparing concordance rates of AMD in monozygotic and dizygotic twins. Results of this study will have direct relevance to the genetic origins of macular degeneration. The ultimate goal is to apply this knowledge to prevent AMD and improve treatment.